Optical device having optical wave guide produced in the presence of acoustic standing wave

ABSTRACT

An electro-acoustic transducer is attached to a block of optical material, and forms an acoustic standing wave in the block; the acoustic standing wave periodically changes the refractive index of the optical material, and forms high refractive index portions alternated with low refractive index portions; and the high refractive index portions serve as optical wave guides, and the electro-acoustic transducer easily produces the optical wave guide in the block.

FIELD OF THE INVENTION

This invention relates to an optical device and, more particularly, toan optical device having an optical wave guide produced in the presenceof acoustic standing wave.

DESCRIPTION OF THE RELATED ART

A typical example of the optical wave guide is an optical fiber. Inorder to confine light in the optical fiber, the optical fiber has amultilayer structure shown in FIG. 1. A core 1a is enclosed in a clad1b, and the core 1a and the clad 1b are, by way of example, formed ofquartz glass and compound glass, respectively. The quartz glass islarger in refractive index than the compound glass, and incident lightL1 repeats the total reflection on the boundary between the core 1a andthe clad 1b. As a result, the light L1 proceeds along the core 1a, andis radiated from the other end. The multilayer structure is achieved bya double crucible pulling down method and so on.

Another example of the optical wave guide is known as "diffusion typeoptical wave guide". The diffusion type optical wave guide has anelongated portion with a large refractive index by replacing an elementof single crystal material with another element. FIG. 2 illustrates thediffusion type optical wave guide. A piece 2a of single crystal compoundof LiNbO₃ is available for the diffusion type optical wave guide, andLi-site of the single crystal material is replaced with H⁺ or Ti³⁺ in anelongated portion 2b indicated by hatching lines. The elongated portion2b is higher in refractive index than the remaining portion 2c of thesingle crystal compound, and serves as a wave guide. Incident light L2is propagated along the elongated portion 2b or the wave guide, and isradiated from the other end.

Another example of the optical wave guide is illustrated in FIG. 3. Theoptical wave guide is categorized in the thin film wave guide, and has aplane wave guide of active material grown by using a liquid-phaseepitaxy. The thin film wave guide increases the energy density ofoptically pumped laser light/oscillation light generated in the activematerial, and, accordingly, improves the oscillation threshold and theslope efficiency or input-and-output characteristics.

FIG. 3 illustrates a thin film wave guide or a planar optical wave guidedisclosed by D. Pelenc et. al. in "High slope efficiency and lowthreshold in a diode-pumped epitaxially grown Yb:YAG wave guide laser",Optics Communications, vol. 115, 1995, pages 491 to 497. A plane waveguide 3a, which is indicated by hatching lines, is sandwiched betweenYb-doped YAG 3b and 3c. Al³⁺ site is partially replaced with Ga³⁺, andthe active material is epitaxially grown on the Yb-doped YAG substrate3b so as to form the plane wave guide 3a. Yb-doped YAG with Ga³⁺ isgrown on the plane wave guide 3a, and the plane wave guide 3a isoverlain by the Yb-doped YAG layer 3c.

Various optical devices have been developed, and several optical devicesare known as "acousto-optic device". An interaction between opticalmaterial and an acoustic wave is known as an acousto-optic effect, andthe acousto-optic effect is available for an optical device.

FIG. 4 illustrates an optical deflector analogous to theelectro-acoustic element disclosed in Japanese Patent Publication ofUnexamined Application No. 50-143547. The optical deflector has anelectro-acoustic transducer 4a attached to a block 4b of optic material.The electro-acoustic transducer 4a generates an ultrasonic wave 4c.

Laser light L3 is obliquely incident onto the block 4b, and ispropagated through the block 4b. The transmitted light L4 is radiatedfrom the block 4b. When the electro-acoustic transducer 4a is driven forgeneration of the ultrasonic wave 4c, Bragg reflection takes place dueto the ultrasonic wave 4c due to an interaction between photon andphonon. If the electro-acoustic transducer 4a changes the frequency ofthe ultrasonic wave 4c, the laser light L3 is diffracted, and isradiated from the block 4b as indicated by L4'.

In this instance, the acoustic wave is applied as a progressive wave. Ifthe acoustic wave does not serve as a progressive wave, the diffractionintensity is drastically decreased, because the interaction between thephoton and phonon causes the diffraction to take place.

A surface acoustic wave is also available for an optical device. FIG. 5illustrates an optical filter for changing the spectrum distribution ofan incident laser light L5. The optical filter is analogous to anoptical deflector with a comb-like electro-acoustic transducer disclosedin Japanese Patent Publication of Unexamined Application No. 62-257133.The filter comprises a block 5a of optical material, an optical waveguide 5b formed on the block 5a and a comb-like electro-acoustictransducer 5c. The comb-like electro-acoustic transducer 5c generates anultrasonic wave 5d, and the laser light L5 is propagated in the opticalwave guide 5b in such a manner as to cross the ultrasonic wave 5d. Thelaser light L5 is radiated from the other side as transmitted light L6.However, when the laser light L5 is interfered with the ultrasonic wave5d, the ultrasonic wave 5d diffracts a predetermined frequency componentL6'. If the electro-acoustic transducer 5c varies the intervals 5e ofthe ultrasonic wave 5d, the filter changes the diffracted frequencycomponent.

The prior art optical wave guide device encounters a problem in theproduction cost. As described hereinbefore, the optical wave guiderequires a refractive index higher than the other portion, and thehigher refractive index is achieved by bonding different materials toeach other, replacing an element of the optical material with anotherelement, diffusing a dopant into an optical element or using ahetero-epitaxy. These modifying techniques are carried out on a part ofthe optical material, and a masking step and/or lithography is necessaryfor the selective modification. This results in a complicatedfabrication process. The complicated fabrication process requiresvarious kinds of apparatus such as, for example, a sputtering apparatus,a thin film growing apparatus, an etching apparatus, a cleaningapparatus and an annealing apparatus. Therefore, the prior art opticaldevice with an optical wave guide is so expensive.

The second problem inherent in the prior art optical wave guide is poorreproducibility. A part of the optical material is converted to a highrefractive index portion through a chemical reaction, and variousparameters dominate the chemical reaction. It is impossible to exactlycontrol all the parameters. For this reason, the reproducibility ispoor.

The third problem is that the prior art optical wave guide can not beformed in all the optical materials. Some optical materials do notwidely change the refractive index, and the crystal structure of anotheroptical material is destroyed through the selective modification.

SUMMARY OF THE INVENTION

It is therefore an important object of the present invention to providean optical device which has an optical wave guide which is inexpensive,reliable and formed in an optical material which is not available forthe prior art optical wave guide.

To accomplish the object, the present invention proposes to partiallychange a refractive index of optical material by using an acousticstanding wave.

In accordance with the present invention, there is provided an opticaldevice comprising a block of optical material, and at least one acousticwave generator for creating an acoustic wave existing as a standing wavein the block, and the standing wave changes a refractive index of a partof the block through an acousto-optic effect so as to form an opticalwave guide in the block.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the optical device according to thepresent invention will be more clearly understood from the followingdescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a cross sectional view showing the structure of the prior artoptical fiber;

FIG. 2 is a perspective view showing the structure of the prior art thinfilm wave guide formed of single crystal of LiNbO₃ ;

FIG. 3 is a perspective view showing the structure of another prior artthin film wave guide having the plane wave guide grown by using theliquid-phase epitaxy;

FIG. 4 is a perspective view showing the structure of the prior artoptical deflector using the acousto-optic effect;

FIG. 5 is a perspective view showing the structure of the prior artoptical filter also using the acousto-optic effect;

FIG. 6 is a perspective view showing the structure of an optical deviceaccording to the present invention;

FIG. 7 is a graph showing a distribution of refractive index generatedby an acoustic standing wave in the optical device;

FIG. 8 is a perspective view showing the structure of another opticaldevice according to the present invention;

FIG. 9 is a perspective view showing the structure of an opticaldeflector according to the present invention;

FIG. 10 is a plan view showing a deflection of laser light incident intothe optical deflector;

FIG. 11 is a plan view showing a frequency filtration achieved by anoptical filter according to the present invention;

FIG. 12 is a perspective view showing the structure of a prior artnonlinear optical element;

FIG. 13 is a perspective view showing the structure of a nonlinearoptical element according to the present invention;

FIG. 14 is a perspective view showing the structure of a solid-statelaser oscillator according to the present invention;

FIG. 15 is a front view showing an optical switch according to thepresent invention;

FIG. 16 is a front view showing a quasi-one dimensional optical waveguide of the optical switch;

FIG. 17 is a perspective view showing a segment where no quasi-onedimensional optical wave guide does not take place;

FIG. 18 is a perspective view showing another segment where thequasi-one dimensional optical wave guide takes place; and

FIG. 19 is a perspective view showing the structure of an optical switchfabricated by the present inventor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Referring to FIG. 6 of the drawings, an optical device embodying thepresent invention comprises a block 6a of optical material and anelectro-acoustic transducer 6b attached to the block 6a. Theelectro-acoustic transducer 6b generates an acoustic wave, and theacoustic wave is propagated in the block 6a. The block 6a has length L0equal to a multiple of the wavelength of the acoustic wave, and astanding wave takes place in the block 6a. The standing wave is stable,and creates a distribution of refractive index as shown in FIG. 7. L1 toL7 in FIG. 7 are corresponding to distance L1 to L7 in FIG. 6. Thestanding wave periodically alternately creates high refractive indexportions 6c, which are indicated by hatching lines, and low refractiveindex portions 6d, and the high refractive index portions 6c are stablein the block 6a. The high refractive index portions 6c and the lowrefractive index portions 6d are alternately laminated, and the highrefractive index portion 6c is available for a planar optical waveguide.

When light L7 is incident on one of the high refractive index portion6c, the light L7 is propagated through the high refractive index portion6c, and is radiated from the other end.

The distribution of refractive index is observed in all the opticalmaterials, and, accordingly, there is no limitation on the opticalmaterial used for the optical device according to the present invention.The variation delta-n of the refractive index due to the acousto-opticeffect is represented by equation 1.

    delta-n.sup.2 =1/2(P.sup.2 n.sup.6 /rho v.sup.3)p          Equation 1

where P is a strain optical coefficient, n is a refractive index, rho isa density, v is an acoustic velocity, and p is an energy of acousticwave.

(P² n⁶ /rho v³) is known as a figure of merit M, and equation 1 isrewritten as

    delta-n.sup.2 =M×p×1/2                         Equation 2

The values of the figure of merit M for various optical materials are,by way of example, taught by Amnon Yariv in "Fundamentals ofOpto-electronics", page 330. The values of the figure of merit are alsotaught by Ogawa et al. in "Crystal Physics and Enginnering".

As will be seen in equation 2, the square of the difference of therefractive index between the high refractive index portion 6c and thelow refractive index portion 6d is proportional to the product of thefigure of merit M and the intensity of the acoustic wave p, and anoptical material with a large figure of merit M achieves a largedifference of the refractive index delta-n between the high refractiveindex portion 6c and the low refractive index portion 6d. When thedifference of the refractive index is of the order of 10⁻³, the highrefractive index portion 6c is available for a planar optical waveguide. Even if an optical material has a relatively small figure ofmerit M, a large input power of the acoustic wave achieves thedifference of refractive index delta-n of the order of 10⁻³.

For example, assuming now that the block 6a is formed of LiNbO₃, whichis used for an optical switch and an optical wavelength convertingelement, the figure of merit M is 7.0 (×10⁻¹⁸ s³ /g). If theelectro-acoustic transducer 6b supplies the acoustic wave at 1kilo-watt/mm². The energy density of the acoustic wave is 1×10⁹ watt/m²=1×10¹² g/s³. Substituting these values for M and p in equation 2.

    delta-n.sup.2 =1/2×(7.0×10.sup.-18)×(1×10.sup.12)

Then, delta-n is 1.8×10⁻³, and the high refractive index portion 6c isavailable for the planar optical wave guide.

On the other hand, if the block 6a is formed of PbMoO₄ or TeO₂ availablefor an optical deflector, the figure of merit M is 73 for PbMoO₄ and 793for TeO₂. Therefore, the planar optical wave guide is created in theblock 6a under the acoustic wave energy of 100 watts and 10 watts,respectively.

As will be appreciated from the foregoing description, the acousticstanding wave alternately creates the high refractive index portions 6cserving as an optical wave guide and the low refractive index portions6d in the block 6a of optical material, and a selective replacement ofan element and a selective diffusion are not required for the opticalwave guide. The location of the high refractive index portion isdetermined by the length L0 and the wavelength of the acoustic wave, andis reproducible. For this reason, the optical device according to thepresent invention is inexpensive and reliable. Finally, theacousto-optic effect is observed in all the optical materials. Even ifan optical material has a relatively small figure of merit, the opticalwave guide is created in the optical material by increasing the inputpower of the electro-acoustic transducer 6b.

Second Embodiment

Turning to FIG. 8 of the drawings, another optical device embodying thepresent invention comprises a cubic block 7a of optical material andelectro-acoustic transducers 7b and 7c attached to two surfaces of thecubic block 7a perpendicular to each other. The electro-acoustictransducer 7b creates a first acoustic standing wave, and the firstacoustic standing wave causes first high refractive index portions 7d toalternate with first low refractive index portions 7e. The first highrefractive index portions 7d are indicated by hatching lines downwardlydrawn from the right side to the left side. On the other hand, the otherelectro-acoustic transducer 7c creates a second acoustic standing wavein a perpendicular direction to that of the first acoustic standingwave. The second acoustic standing wave causes second high refractiveindex portions 7f to alternate with second low refractive index portions7g. The second high refractive index portions 7f are indicated byhatching lines downwardly drawn from the left side to the right side.

The first high refractive index portions 7d and the second highrefractive index portions 7f form intersections 7h indicated by bothhatching lines, and the intersections 7h serve as quasi-one dimensionaloptical wave guides. When light L8 is incident onto one of the quasi-onedimensional optical wave guide 7h, the light is propagated through thequasi-one dimensional optical wave guide without a diffusion, and isradiated from the other side.

Although the cubic block 7a is used for the optical device, it is notnecessary for the optical device to have one length measured in theperpendicular direction to the electro-acoustic transducer 7b equal tothe other length measured in the perpendicular direction to the otherelectro-acoustic transducer 7c. The one length may and the other lengthmay be equal to one multiple of the wavelength and another multiple ofthe wavelength different from each other.

The optical device shown in FIG. 8 is also inexpensive and reliable, andmost of the optical materials are available for the optical device.

EXAMPLES

The optical device shown in FIG. 6 and the optical device shown in FIG.8 are two kinds of basic structure of the optical device according tothe present invention. Various kinds of optical devices are fabricatedon the basis of the two kinds of basic structure as follows.

First Example

FIGS. 9 and 10 illustrate an optical deflector. The optical deflectorcomprises a block 8a of optical material, a first electro-acoustictransducer 8b attached to an upper surface of the block 8a and a secondelectro-acoustic transducer 8c attached to a side surface of the block8a. The first electro-acoustic transducer 8b generates a first acousticwave, and the first acoustic wave is supplied to the block 8a. The block8a has a height equal to a multiple of the wavelength of the firstacoustic wave, and a standing wave takes place in the direction of theheight. The standing wave periodically changes the refractive index ofthe block 8a, and high refractive index portions 8d are alternated withlow refractive index portions 8e. The high refractive index portions 8dare indicated by hatching lines.

The second electro-acoustic transducer 8c is aligned with one of thehigh refractive index portions 8d serving as a planar optical waveguide, and generates a second acoustic wave 8f. A progressive wave takesplace in a perpendicular direction to that of the standing wave. Whenlaser light L9 is incident onto the planar optical wave guide 8d, thelaser light L9 is propagated through the planar optical wave guide 8d,and laser light L10 is radiated from the other side. However, when thesecond electro-acoustic transducer 8c changes the frequency of thesecond acoustic wave, the progressive wave causes the laser light L9 tochange the direction due to Bragg reflection, and laser light L10' isradiated from the other side as shown in FIG. 10.

The present inventor formed the block 8a of PbMoO₄, and the first andsecond electro-acoustic transducers 8b and 8c are attached to the uppersurface and the side surface of the block 8a as shown in FIGS. 9 and 10.The first electro-acoustic transducer 8b generated the first ultrasonicwave at 30 MHz, and the wavelength was 100 microns. The height of theblock 8a was regulated to a multiple of 100 microns, and thedistribution of refractive index was repeated at intervals of 100microns.

The present inventor confirmed the following phenomena. While the secondelectro-acoustic transducer 8c was standing idle, the incident laserlight L9 straightly proceeded, and the laser light L10 was radiated fromthe other side. When the Bragg condition were satisfied, the incidentlaser light L9 was deflected, and the laser light L10' was radiated fromthe other side.

Second Example

An optical frequency filter according to the present invention issimilar in structure to the optical deflector shown in FIG. 9, andcomprises a block 9a of optical material, a first electro-acoustictransducer 9b attached to an upper surface of the block 9a and a secondelectro-acoustic transducer 9c attached to a side surface of the block9a as shown in FIG. 11. The height of the block 9a is equal to amultiple of the wavelength of an acoustic wave generated by the firstelectro-acoustic transducer 9b. Therefore, the acoustic wave exists asan acoustic standing wave, and the acoustic standing wave creates highrefractive index portions and low refractive index portions in the block9a. The high refractive index portions are alternated with the lowrefractive index portions, and the second electro-acoustic transducer 9cis aligned with one of the high refractive index portions serving as anoptical wave guide. The second electro-acoustic transducer 9c generatesultrasonic, and the ultrasonic exists as a progressive wave 9d.

Assuming now that light components different in wavelength form anoptical beam L10, the light beam L10 is incident into the optical waveguide, and is propagated along the optical wave guide. A light componentsatisfies the Bragg condition, and is diffracted as indicated bydots-and-dash line L11. However, the other light components L11' do notsatisfy the Bragg condition, and are radiated from the other side.

The present inventor fabricated the optical frequency filter shown inFIG. 11, and the block 9a was formed of MoPbO₄. The present inventorchanged the frequency of the progressive wave, and measured thewavelength of the diffracted light component L11. The present inventorconfirmed that the diffracted light component L11 satisfied the Braggcondition.

Third Example

The present invention is applied to a nonlinear optical wave guide.Nonlinear optical material is available for a wavelength conversiondevice. When increasing the energy density of incident laser light, theconversion efficiency is enhanced. For this reason, the incident laserlight L12 is usually focused by using a lens unit (not shown), and ahigh energy density zone 10a takes place in the nonlinear optical waveguide (see FIG. 12). However, the other zone is not so high in theenergy density. This results in that only a small part of the nonlinearoptical wave guide is used for the wavelength converter.

When an angular phase matching technique is used, an angularmisalignment takes place, and angle AGL1 makes the fundamental wave andthe harmonics different in phase. For this reason, it is preferable forthe incident laser light L12 to be propagated as a parallel light.

FIG. 13 illustrates a wavelength conversion device formed of nonlinearoptical material and embodying the present invention. The wavelengthconversion device comprises a block 11a of nonlinear optical material, afirst electro-acoustic transducer 11b attached to the upper surface ofthe block 11a and a second electro-acoustic transducer 11c attached to aside surface of the block 11a.

A bulk of nonlinear optical material (not shown) is cut into the block11a under the angular phase matching condition. The firstelectro-acoustic transducer 11b generates a first acoustic wave, and theblock 11a has a height equal to a multiple of the wavelength of thefirst acoustic wave. The second electro-acoustic transducer 11c alsogenerates a second acoustic wave, and the block 11a has a width equal toanother multiple of the wavelength of the second acoustic wave. Thefirst acoustic wave exist as a first standing wave, and high refractiveindex portions and low refractive index portions alternately take placein the direction of the height. Similarly, the second acoustic waveexists as a second standing wave, and high refractive index portions arealternated with low refractive index portions in the direction of thewidth. The high refractive index portions due to the first standing waveare indicated by hatching lines downwardly drawn from the right side tothe left side in FIG. 13. On the other hand, the high refractive indexportions due to the second standing wave are indicated by hatching linesdownwardly drawn from the left side to the right side in FIG. 13. Thehigh refractive index portions due to the first standing wave areintersected with the high refractive index portions due to the secondstanding wave, and the intersections serve as quasi-one dimensionaloptical wave guides.

Assuming now that a lens unit (not shown) focuses a laser light beam L13upon one of the quasi-one dimensional optical wave guide, the quasi-onedimensional optical wave guide propagates the laser beam L13 withoutdiffusion, and the laser beam L13 is assumed to be a parallel light inthe quasi-one dimensional optical wave guide. Therefore, the laser beamL13 maintains the high energy density over the quasi-one dimensionaloptical wave guide, and the wavelength of the laser beam L13 iseffectively converted to a light beam L14 with a different wavelength.

The present inventor fabricated the optical wavelength converter shownin FIG. 13. The block 11a was formed of Li₂ B₄ O₇. Li₂ B₄ O₇ can convertthe wavelength until the ultra-violet region. The wavelength converterwas expected to convert the second harmonic of YAG laser at 532millimeters to FHG light at 266 millimeters, and a bulk of Li₂ B₄ O₇ wascut at AGL1=45 degrees for the angular phase matching. The firstelectro-acoustic transducer 11b and the second electro-acoustictransducer 11c are bonded to the upper and the side surfaces of theblock 11a. The first electro-acoustic transducer 11b and the secondelectro-acoustic transducer 11c may be attached to the upper and sidesurfaces by using a sputtering.

The acoustic velocity is 5000 meters per second in the crystal of Li₂ B₄O₇, and the first and second electro-acoustic transducers 11b/11coscillated at 5 MHz. Then, the change of refractive index took place atintervals of 100 microns. The first and second electro-acoustictransducers 11b and 11c were driven at 1 kilo-watt for generation of thefirst and second acoustic waves, and the high refractive index portionwas larger in refractive index than the low refractive index portion by3 to 10. The quasi-optical wave guide was 15 millimeters long.

The present inventor further fabricated the prior art optical wavelengthconverter shown in FIG. 12. The same nonlinear optical material wasused, and the prior art optical wavelength converter was also expectedto convert the second harmonic of the YAG laser to the FHG light beam.

A lens unit (not shown) was provided between the YAG laser source (notshown) and the optical wavelength converters shown in FIGS. 12 and 13,and had a focal length of 100 millimeters. The incident laser beam L13had a diameter of the order of 50 microns at the focal point.

The YAG laser source radiated the laser light at 10 Hz, and the power ofthe second harmonic of 532 nanometer wavelength was averaged at 8milli-watt for 10 nano-second. The optical wavelength converteraccording to the present invention radiated the FHG light beam of 266nanometer wavelength at 1 milli-watt. On the other hand, the prior artoptical wavelength converter radiated the FHG light beam at 100micro-watt. Thus, the optical wavelength converter according to thepresent invention achieved the high converting efficiency ten timeslarger than that of the prior art optical wavelength converter.

The present inventor further fabricated the optical wavelength converterof another nonlinear optical material, and confirmed the improvement ofthe converting efficiency.

Fourth Example

While a laser diode is being excited through an optical pumping, anoptical resonator increases the energy density of the excited/oscillatedlight. The increase of energy density results in a decrease of anoscillation threshold, and an increase of the slope efficiency.Especially, in case of three-level laser oscillation, these phenomenaare appreciated, because the oscillation threshold is high.

FIG. 14 illustrates a laser oscillator embodying the present invention.The laser oscillator comprises a block 12a of Yb-doped YVO₄, anelectro-acoustic transducer 12b attached to an upper surface of theblock 12a and Ar coating/HR coating 12c for a laser diode/oscillatedlaser light. Yb-doped YVO₄ is a three level laser oscillating material,and has a high oscillation threshold, and Yb absorbs the light componentof 900 nanometer wavelength.

The acoustic velocity is 5000 meters per second in the crystal of YVO₄,and the electro-acoustic transducer 12b generates an acoustic wave at100 MHz. The block 12a has a height equal to a multiple of thewavelength of the acoustic wave. The acoustic wave exists as a standingwave, and high refractive index portions 12d and low refractive indexportions 12e alternately take place in the block 12a. The highrefractive index portions 12d are indicated by hatching lines, and serveas optical wave guide of 50 microns thick. A part of oscillated lightL16 is taken out from the opposite side surface through an output mirror13.

When a laser diode radiates excited laser light L15 to one of the highrefractive index portions 12d, the excited laser light/oscillated laserlight L15/L16 are confined in the high refractive index portion 12d, andthe energy density increases. The laser oscillator is continuouslyoscillating, and the absorption efficiency and the luminous efficiencyare improved.

The present inventor fabricated the laser oscillator describedhereinbefore, and the laser diode is excited at 500 milli-watt. Thelaser oscillator achieved an output of 1.03 micron oscillation light at50 milli-watt.

The present inventor confirmed the same effects by using other lasermaterials.

Fifth Embodiment

FIG. 15 illustrates an optical switch embodying the present invention.The optical switch comprises a block 13a of optical material, firstelectro-acoustic transducers 13b1/13b1', 13b2/13b2', 13b3/13b3' and13b4/13b4' attached to upper/lower surfaces of the block 13a and secondelectro-acoustic transducers 13c1/13c1', 13c2/13c2', 13c3/13c3' and13c4/13c4' attached to the side surfaces of the block 13a. Thedimensions of the block 13a are adjusted in such a manner that the firstand second electro-acoustic transducers 13b1/13b1' to 13b4/13b4' and13c1/13c1' to 13c4/13c4' generate standing waves in the directionsperpendicular to each other. The first electro-acoustic transducers13b1/13b1' to 13b4/13b4' and the second electro-acoustic transducers13c1/13c1' to 13c4/13c4' define a matrix of segments SG11, . . . ,SG14,. . . and SG41, . . . SG44 in the block 13a as shown in FIG. 16, andeach segment SG11 to SG44 extends between a front surface to the rearsurface of the block 13a. High refractive index portions are alignedwith the center lines of the segments SG11 to SG44, and quasi-ondimensional optical wave guides selectively take place in the segmentsSG11 to SG44.

When the first electro-acoustic transducer 13b2 and the secondelectro-acoustic transducer 13c3' are driven for generating the standingwaves, the first electro-acoustic transducer 13b2 and the secondelectro-acoustic transducer 13c3' create the high refractive indexportions indicated by hatching lines downwardly drawn from the rightside to the left side and the high refractive index portions indicatedby hatching lines downwardly drawn from the left side to the right side,and the quasi-one dimensional optical wave guide takes place in thesegment SG32.

While the quasi-one dimensional optical wave guide is not being formedin the segment SG32, an incident laser light beam L17 focused on thesegment SG32 is diffused as shown in FIG. 17, and the laser light beamL17 is never radiated from the other end. On the other hand, when thequasi-one dimensional optical wave guide 13d is produced in the segmentSG32, the laser beam L17 is propagated through the quasi-one dimensionaloptical wave guide 13d, and is radiated from the other end as shown inFIG. 18.

The present inventor fabricated the optical switch shown in FIG. 19. Theblock 13a was formed of Te glass. Te glass had a large acousto-opticalfigure of merit of the order of 30, and was optically isotropic, Theblock 13a had the front and rear surfaces measured by 4 millimeters×4millimeters, and the front surface was spaced from the rear surface by30 millimeters. The acoustic velocity was 3400 meters per second in Teglass, and the first electro-acoustic transducers 13b1/13b1' to13b4/13b4' and the second electro-acoustic transducers 13c1/13c1' to13c4/13c4' were driven at 3.4 MHz. The quasi-one dimensional opticalwave guides were selectively formed in the segments SG11 to SG44 of 1millimeter square.

A micro-lens unit (not shown) was provided between a laser diode (notshown) and the optical switch, and the micro-lens unit focused the laserlight on the central zones of the segments SG11 to SG44. The presentinventor confirmed a switching action of the 4×4 optical switch.

Although particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatvarious changes and modifications may be made without departing from thespirit and scope of the present invention.

For example, the number of electro-acoustic transducers may be differentfrom those of the examples, and the first to fifth examples do not limitthe dimensions of the optical devices according to the presentinvention.

What is claimed is:
 1. An optical device comprising a block of opticalmaterial, at least one acoustic wave generator for creating an acousticwave in said block, wherein said acoustic wave is a standing wavechanging a refractive index of a part of said block through anacoustic-optic effect so as to form an optical wave guide in said block,and wherein said block of optical material has a length measured in adirection parallel to said standing wave, and said length is equal to amultiple of the wavelength of said acoustic wave.
 2. An optical devicecomprising a block of optical material, at least one acoustic wavegenerator for creating an acoustic wave in said block, wherein saidacoustic wave is a standing wave changing a refractive index of a partof said block through an acoustic-optic effect so as to form an opticalwave guide in said block, and said optical wave guide is a planaroptical wave guide substantially perpendicular to said standingwave;said optical device further comprising another acoustic wavegenerator for generating another acoustic wave existing as a progressivewave, said progressive wave being propagated through said planar opticalwave guide so as to deflect an incident light.
 3. The optical device asset forth in claim 2, in which said incident light contains a pluralityof light components different in wavelength from one another, and saidprogressive wave selectively deflects said plurality of light componentsunder Bragg condition.
 4. An optical device comprising a block ofoptical material, at least one acoustic wave generator for creating anacoustic wave in said block, wherein said acoustic wave is a standingwave changing a refractive index of a part of said block through anacoustic-optic effect so as to form an optical wave guide in said block,and said block is formed of a nonlinear optical material;said opticaldevice further comprising another acoustic wave generator for generatinganother acoustic wave existing as another standing wave in said block ina direction perpendicular to the direction of said standing wave, saidstanding wave and said another standing wave forming at least onequasi-one dimensional optical wave guide in a portion of said blockwhere both of said standing wave and said another standing wave increasesaid refractive index.
 5. The optical device as set forth in claim 4, inwhich said block is cut from a bulk of said nonlinear optical materialunder an angular phase matching condition, and said quasi-onedimensional optical wave guide converts an incident laser light toanother light beam different in wavelength from said incident laserlight.
 6. An optical device comprising a block of optical material, atleast one acoustic wave generator for creating an acoustic wave in saidblock, wherein said acoustic wave is a standing wave changing arefractive index of a part of said block through an acousto-optic effectso as to form an optical wave guide in said block, and wherein saidoptical material is available for a laser oscillation, and a coatingfilm is attached to said block so as to confine an excited laser lightsupplied from the outside thereof in said optical wave guide forincreasing an energy density of said excited laser light and anoscillated laser light.
 7. The optical device as set forth in claim 6,in which said optical material is Yb-doped YVO₄.
 8. An optical devicecomprising a block of optical material, at least one acoustic wavegenerator for creating an acoustic wave in said block, wherein saidacoustic wave is a standing wave changing a refractive index of a partof said block through an acousto-optic effect so as to form an opticalwave guide in said block, and wherein a plurality of first acousticsub-generators, independently driven for generating said acoustic wave,form in combination said at least one acoustic wave generator,saidoptical device further comprising a plurality of second acousticsub-generators independently driven for generating another acoustic waveexisting as another standing wave perpendicular to said standing wave insaid block, said plurality of first acoustic sub-generators and saidplurality of second acoustic sub-generators defining a matrix ofsegments in said block where at least one quasi-one dimensional opticalwave guide selectively takes place.